Abstract

Immunogenic cell death (ICD) is the process by which certain cytotoxic drugs induce apoptosis of tumor cells in a manner that stimulates the immune system. In this study, we investigated whether ADCs conjugated with pyrrolobenzodiazepine dimer (PBD) or tubulysin payloads induced ICD, modulated the immune microenvironment, and could combine with IO drugs to enhance antitumor activity. We show that these payloads on their own induced an immune response that prevented the growth of tumors following subsequent tumor cell challenge. ADCs had greater antitumor activity in immunocompetent vs. immunodeficient mice, demonstrating a contribution of the immune system to the antitumor activity of these ADCs. These ADCs also induced immunological memory. In the CT26 model, depletion of CD8+ T cells abrogated the activity of these ADCs when used alone or in combination with a PD-L1 antibody, confirming a role for T cells in the antitumor activity. Combinations of ADCs in different tumor models with IO drugs including PD-1 or PD-L1 antibodies, or OX40 ligand or GITR ligand fusion proteins produced synergistic antitumor responses. Importantly, synergy was observed in some cases with suboptimal doses of ADCs, potentially providing an approach to achieve potent antitumor responses while minimizing ADC-induced toxicity. Immunophenotyping studies in different tumor models revealed broad immunomodulation of lymphoid and myeloid cells by ADCs and ADC/IO combinations. These results suggest that it may be possible to develop novel combinatorial therapies with PBD- and tubulysin-based ADCs and IO drugs that may increase clinical responses.